System and Method of Protecting an HVAC System

ABSTRACT

Systems and methods are provided for operating a heating, ventilation, and/or air conditioning (HVAC) system that include recording a number of consecutive occasions in which a defrost mode is entered within a first predefined length of time after a heating cycle is entered, preventing operation of at least one component of the HVAC system for a second predefined length of time in response to entering the defrost mode a first predetermined consecutive number of occurrences within the first predefined length of time after a heating cycle is entered, recording a number of consecutive preventions of operation of the component of the HVAC system, and determining that a fault condition exists in the HVAC system in response to the number of consecutive temporary preventions of operation of the component of the HVAC system exceeding a second predefined number of occurrences.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/933,748 filed on Jan. 30, 2014 by George William Brandt, et al., and entitled “System and Method of Protecting an HVAC System,” the disclosure of which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Heating, ventilation, and air conditioning systems (HVAC systems) may be used to heat and/or cool comfort zones to comfortable temperatures. Comfort zones are often the occupiable portions of residential and/or commercial areas and may be subject to variable zone conditions, such as temperature and humidity. A portion of an HVAC system may be installed outdoors or in some other location remote from the comfort zone for the purpose of performing heat exchange. Such a location may be referred to as an ambient zone and may also have variable temperature and humidity conditions.

Some HVAC systems are heat pump systems. Heat pump systems are generally capable of operating in a cooling mode in which a comfort zone is cooled by transferring heat from the comfort zone to an ambient zone using a refrigeration cycle (e.g., the Rankine cycle). Heat pump systems are also generally capable of operating in a heating mode in which the direction of refrigerant flow through the components of the HVAC system is reversed so that heat is transferred from the ambient zone to the comfort zone, thereby heating the comfort zone. Heat pump systems generally use a reversing valve for rerouting the direction of refrigerant flow between the compressor and the heat exchangers associated with the comfort zone and the ambient zone.

If moisture is present in an ambient zone, the moisture may condense on the ambient zone components of an HVAC system. Accordingly, when the temperature in the ambient zone is sufficiently low, frost and/or ice may accumulate on the outdoor components of the HVAC system, sometimes necessitating a defrosting of the components of the HVAC system on which frost and/or ice have accumulated. In a heat pump system, the defrosting may be achieved by reversing the direction of refrigerant flow from the direction of flow used in the heating mode. Specifically, the refrigerant flow is such that heat is transferred from the comfort zone to the ambient zone during the defrosting of the HVAC system components.

SUMMARY

In some embodiments, a method of operating a heating, ventilation, and/or air conditioning (HVAC) system is disclosed as comprising: detecting a fault condition in response to the HVAC system to entering a defrost mode before a predefined threshold is reached for a predefined number of consecutive occasions; and preventing operation of at least one component of the HVAC system for a predefined length of time in response to detecting the fault condition.

In other embodiments, a heating, ventilation, and/or air conditioning (HVAC) system is disclosed as comprising: a system controller configured to: detect a fault condition in response to the HVAC system to entering a defrost mode before a predefined threshold is reached for a predefined number of consecutive occasions; and prevent operation of at least one component of the HVAC system for a predefined length of time in response to detecting the fault condition.

In yet other embodiments, a method for operating a heating, ventilation, and/or air conditioning (HVAC) system is disclosed as comprising: recording a number of consecutive occasions in which a defrost mode is entered within a first predefined length of time after a heating cycle is entered; preventing operation of at least one component of the HVAC system for a second predefined length of time in response to entering the defrost mode a first predetermined consecutive number of occurrences within the first predefined length of time after a heating cycle is entered; recording a number of consecutive preventions of operation of the component of the HVAC system; and determining that a fault condition exists in the HVAC system in response to the number of consecutive temporary preventions of operation of the component of the HVAC system exceeding a second predefined number of occurrences.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description:

FIG. 1 is a schematic diagram of an HVAC system according to an embodiment of the disclosure;

FIG. 2 is a schematic diagram of the air circulation paths of the HVAC system of FIG. 1;

FIG. 3 is a flowchart of a method for shutting down an HVAC system; and

FIG. 4 is a representation of a general-purpose processor (e.g., electronic controller or computer) system suitable for implementing the embodiments of the disclosure.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an HVAC system 100 according to an embodiment of this disclosure. HVAC system 100 comprises an indoor unit 102, an outdoor unit 104, and a system controller 106. In some embodiments, the system controller 106 may operate to control operation of the indoor unit 102 and/or the outdoor unit 104. As shown, the HVAC system 100 is a so-called heat pump system that may be selectively operated to implement one or more substantially closed thermodynamic refrigeration cycles to provide a cooling functionality and/or a heating functionality. In other embodiments, the HVAC system 100 may be some other type of heating, ventilation, and/or air conditioning system.

The indoor unit 102 comprises an indoor heat exchanger 108, an indoor fan 110, and an indoor metering device 112. The indoor heat exchanger 108 may be a plate fin heat exchanger configured to allow heat exchange between refrigerant carried within internal tubing of the indoor heat exchanger 108 and fluids that contact the indoor heat exchanger 108 but that are kept segregated from the refrigerant. In other embodiments, the indoor heat exchanger 108 may comprise a spine fin heat exchanger, a microchannel heat exchanger, or any other suitable type of heat exchanger.

The indoor fan 110 may be a centrifugal blower comprising a blower housing, a blower impeller at least partially disposed within the blower housing, and a blower motor configured to selectively rotate the blower impeller. In other embodiments, the indoor fan 110 may comprise a mixed-flow fan and/or any other suitable type of fan. The indoor fan 110 may be configured as a modulating and/or variable speed fan capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the indoor fan 110 may be configured as a multiple speed fan capable of being operated at a plurality of operating speeds by selectively electrically powering different ones of multiple electromagnetic windings of a motor of the indoor fan 110. In yet other embodiments, the indoor fan 110 may be a single speed fan.

The indoor metering device 112 may be an electronically controlled motor driven electronic expansion valve (EEV). In alternative embodiments, the indoor metering device 112 may comprise a thermostatic expansion valve, a capillary tube assembly, and/or any other suitable metering device. The indoor metering device 112 may comprise and/or be associated with a refrigerant check valve and/or refrigerant bypass for use when a direction of refrigerant flow through the indoor metering device 112 is such that the indoor metering device 112 is not intended to meter or otherwise substantially restrict flow of refrigerant through the indoor metering device 112.

The outdoor unit 104 comprises an outdoor heat exchanger 114, a compressor 116, an outdoor fan 118, an outdoor metering device 120, and a reversing valve 122. The outdoor heat exchanger 114 may be a spine fin heat exchanger configured to allow heat exchange between refrigerant carried within internal passages of the outdoor heat exchanger 114 and fluids that contact the outdoor heat exchanger 114 but that are kept segregated from the refrigerant. In other embodiments, the outdoor heat exchanger 114 may comprise a plate fin heat exchanger, a microchannel heat exchanger, or any other suitable type of heat exchanger.

The compressor 116 may be a multiple speed scroll type compressor configured to selectively pump refrigerant at a plurality of mass flow rates. In alternative embodiments, the compressor 116 may be a modulating compressor capable of operation over one or more speed ranges, a reciprocating type compressor, a single speed compressor, and/or any other suitable refrigerant compressor and/or refrigerant pump.

The outdoor fan 118 may be an axial fan comprising a fan blade assembly and fan motor configured to selectively rotate the fan blade assembly. In other embodiments, the outdoor fan 118 may comprise a mixed-flow fan, a centrifugal blower, and/or any other suitable type of fan and/or blower. The outdoor fan 118 may be configured as a modulating and/or variable speed fan capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the outdoor fan 118 may be configured as a multiple speed fan capable of being operated at a plurality of operating speeds by selectively electrically powering different ones of multiple electromagnetic windings of a motor of the outdoor fan 118. In yet other embodiments, the outdoor fan 118 may be a single speed fan.

The outdoor metering device 120 may be a thermostatic expansion valve. In alternative embodiments, the outdoor metering device 120 may comprise an electronically controlled motor driven EEV, a capillary tube assembly, and/or any other suitable metering device. The outdoor metering device 120 may comprise and/or be associated with a refrigerant check valve and/or refrigerant bypass for use when a direction of refrigerant flow through the outdoor metering device 120 is such that the outdoor metering device 120 is not intended to meter or otherwise substantially restrict flow of refrigerant through the outdoor metering device 120.

The reversing valve 122 may be a so-called four-way reversing valve. The reversing valve 122 may be selectively controlled to alter a flow path of refrigerant in the HVAC system 100 as described in greater detail below. The reversing valve 122 may comprise an electrical solenoid or other device configured to selectively move a component of the reversing valve 122 between operational positions.

The system controller 106 may comprise a touchscreen interface for displaying information and for receiving user inputs. The system controller 106 may display information related to the operation of the HVAC system 100 and may receive user inputs related to operation of the HVAC system 100. The system controller 106 may further be operable to display information and receive user inputs tangentially related and/or unrelated to operation of the HVAC system 100. In some embodiments, the system controller 106 may comprise a temperature sensor and may further be configured to control heating and/or cooling of zones associated with the HVAC system 100. In some embodiments, the system controller 106 may be configured as a thermostat for controlling the supply of conditioned air to zones associated with the HVAC system 100.

In some embodiments, the system controller 106 may selectively communicate with an indoor controller 124 of the indoor unit 102, with an outdoor controller 126 of the outdoor unit 104, and/or with other components of the HVAC system 100. In some embodiments, the system controller 106 may be configured for selective bidirectional communication over a communication bus 128. In some embodiments, portions of the communication bus 128 may comprise a three-wire connection suitable for communicating messages between the system controller 106 and one or more of the HVAC system components configured for interfacing with the communication bus 128.

Still further, the system controller 106 may be configured to selectively communicate with HVAC system components and/or another device 130 via a communication network 132. In some embodiments, the communication network 132 may comprise a telephone network and the other device 130 may comprise a telephone. In some embodiments, the communication network 132 may comprise the Internet and the other device 130 may comprise a so-called smartphone and/or other Internet-enabled mobile telecommunication device.

The indoor controller 124 may be carried by the indoor unit 102 and may be configured to receive information inputs, transmit information outputs, and otherwise communicate with the system controller 106, the outdoor controller 126, and/or any other device via the communication bus 128 and/or any other suitable medium of communication. In some embodiments, the indoor controller 124 may be configured to communicate with an indoor personality module 134, receive information related to a speed of the indoor fan 110, transmit a control output to an electric heat relay, transmit information regarding an indoor fan volumetric flow rate, communicate with and/or otherwise affect control over an air cleaner 136, and communicate with an indoor EEV controller 138. In some embodiments, the indoor controller 124 may be configured to communicate with an indoor fan controller 142 and/or otherwise affect control over operation of the indoor fan 110. In some embodiments, the indoor personality module 134 may comprise information related to the identification and/or operation of the indoor unit 102 and/or a position of the outdoor metering device 120.

In some embodiments, the indoor EEV controller 138 may be configured to receive information regarding temperatures and pressures of the refrigerant in the indoor unit 102. More specifically, the indoor EEV controller 138 may be configured to receive information regarding temperatures and pressures of refrigerant entering, exiting, and/or within the indoor heat exchanger 108. Further, the indoor EEV controller 138 may be configured to communicate with the indoor metering device 112 and/or otherwise affect control over the indoor metering device 112.

The outdoor controller 126 may be carried by the outdoor unit 104 and may be configured to receive information inputs, transmit information outputs, and otherwise communicate with the system controller 106, the indoor controller 124, and/or any other device via the communication bus 128 and/or any other suitable medium of communication. In some embodiments, the outdoor controller 126 may be configured to communicate with an outdoor personality module 140 that may comprise information related to the identification and/or operation of the outdoor unit 104. In some embodiments, the outdoor controller 126 may be configured to receive information related to an ambient temperature associated with the outdoor unit 104, information related to a temperature of the outdoor heat exchanger 114, and/or information related to refrigerant temperatures and/or pressures of refrigerant entering, exiting, and/or within the outdoor heat exchanger 114 and/or the compressor 116. In some embodiments, the outdoor controller 126 may be configured to transmit information related to monitoring, communicating with, and/or otherwise affecting control over the outdoor fan 118, a compressor sump heater, a solenoid of the reversing valve 122, a relay associated with adjusting and/or monitoring a refrigerant charge of the HVAC system 100, a position of the indoor metering device 112, and/or a position of the outdoor metering device 120. The outdoor controller 126 may further be configured to communicate with a compressor drive controller 144 that is configured to electrically power and/or control the compressor 116.

The HVAC system 100 is shown configured for operating in a so-called cooling mode in which heat is absorbed by refrigerant at the indoor heat exchanger 108 and heat is rejected from the refrigerant at the outdoor heat exchanger 114. In some embodiments, the compressor 116 may be operated to compress refrigerant and pump the relatively high temperature and high pressure compressed refrigerant from the compressor 116 through the reversing valve 122 to the outdoor heat exchanger 114. As the refrigerant is passed through the outdoor heat exchanger 114, the outdoor fan 118 may be operated to move air into contact with the outdoor heat exchanger 114, thereby transferring heat from the refrigerant to the air surrounding the outdoor heat exchanger 114. The refrigerant may primarily comprise liquid phase refrigerant and the refrigerant may be pumped from the outdoor heat exchanger 114 to the indoor metering device 112 through and/or around the outdoor metering device 120, which does not substantially impede flow of the refrigerant in the cooling mode. The indoor metering device 112 may meter passage of the refrigerant through the indoor metering device 112 so that the refrigerant downstream of the indoor metering device 112 is at a lower pressure than the refrigerant upstream of the indoor metering device 112. The pressure differential across the indoor metering device 112 allows the refrigerant downstream of the indoor metering device 112 to expand and/or at least partially convert to a gaseous phase. The gaseous phase refrigerant may enter the indoor heat exchanger 108. As the refrigerant is passed through the indoor heat exchanger 108, the indoor fan 110 may be operated to move air into contact with the indoor heat exchanger 108, thereby transferring heat to the refrigerant from the air surrounding the indoor heat exchanger 108. The refrigerant may thereafter reenter the compressor 116 after passing through the reversing valve 122.

To operate the HVAC system 100 in the so-called heating mode, the reversing valve 122 may be controlled to alter the flow path of the refrigerant, the indoor metering device 112 may be disabled and/or bypassed, and the outdoor metering device 120 may be enabled. In the heating mode, refrigerant may flow from the compressor 116 to the indoor heat exchanger 108 through the reversing valve 122. The refrigerant may be substantially unaffected by the indoor metering device 112 and may experience a pressure differential across the outdoor metering device 120. The refrigerant may pass through the outdoor heat exchanger 114 and reenter the compressor 116 after passing through the reversing valve 122. In general, operation of the HVAC system 100 in the heating mode reverses the roles of the indoor heat exchanger 108 and the outdoor heat exchanger 114 as compared to their operation in the cooling mode.

The HVAC system 100 is shown as a so-called split system, wherein the indoor unit 102 is located separately from the outdoor unit 104. Alternative embodiments of an HVAC system may comprise a so-called package system in which one or more of the components of the indoor unit 102 and one or more of the components of the outdoor unit 104 are carried together in a common housing or package. The HVAC system 100 is shown as a so-called ducted system where the indoor unit 102 is located remote from the conditioned zones, thereby requiring air ducts to route the circulating air. However, in alternative embodiments, an HVAC system may be configured as a non-ducted system in which the indoor unit 102 and/or multiple indoor units 102 associated with an outdoor unit 104 are located substantially in the space and/or zone to be conditioned by the respective indoor units 102, thereby not requiring air ducts to route the air conditioned by the indoor units 102.

Referring now to FIG. 2, a schematic diagram of the air circulation paths for a structure 200 conditioned by two HVAC systems 100 is shown. In this embodiment, the structure 200 is conceptualized as comprising a lower floor 202 and an upper floor 204. The lower floor 202 comprises zones 206, 208, and 210, while the upper floor 204 comprises zones 212, 214, and 216. The HVAC system 100 associated with the lower floor 202 is configured to circulate and/or condition air of lower zones 206, 208, and 210, while the HVAC system 100 associated with the upper floor 204 is configured to circulate and/or condition air of upper zones 212, 214, and 216.

In addition to the components of the HVAC system 100 described above, in this embodiment, each HVAC system 100 further comprises a ventilator 146, a prefilter 148, a humidifier 150, and a bypass duct 152. The ventilator 146 may be operated to selectively exhaust circulating air to the environment and/or introduce environmental air into the circulating air. The prefilter 148 may generally comprise a filter medium selected to catch and/or retain relatively large particulate matter prior to air exiting the prefilter 148 and entering the air cleaner 136. The humidifier 150 may be operated to adjust the humidity of the circulating air. The bypass duct 152 may be utilized to regulate air pressures within the ducts that form the circulating air flow paths. In some embodiments, air flow through the bypass duct 152 may be regulated by a bypass damper 154, while air flow delivered to the zones 206, 208, 210, 212, 214, and 216 may be regulated by zone dampers 156.

Each HVAC system 100 may further comprise a zone thermostat 158 and a zone sensor 160. In some embodiments, a zone thermostat 158 may communicate with the system controller 106 and may allow a user to control a temperature, humidity, and/or other environmental setting for the zone in which the zone thermostat 158 is located. Further, the zone thermostat 158 may communicate with the system controller 106 to provide temperature, humidity, and/or other environmental feedback regarding the zone in which the zone thermostat 158 is located. In some embodiments, a zone sensor 160 may communicate with the system controller 106 to provide temperature, humidity, and/or other environmental feedback regarding the zone in which the zone sensor 160 is located.

The system controllers 106 may be configured for bidirectional communication with each other and may further be configured so that a user may, using either of the system controllers 106, monitor and/or control any of the HVAC system components regardless of which zones the components may be associated with. Further, each system controller 106, each zone thermostat 158, and each zone sensor 160 may comprise a humidity sensor. As such, it will be appreciated that structure 200 may be equipped with a plurality of humidity sensors in a plurality of different locations. In some embodiments, a user may effectively select which of the plurality of humidity sensors is used to control operation of one or more of the HVAC systems 100.

If the outdoor temperature is sufficiently low, ice or frost may form on the outdoor components of outdoor unit 104 of the HVAC system 100, such as the coils in the outdoor heat exchanger 114. To prevent or mitigate the formation of ice or frost on the outdoor components of the HVAC system 100, the HVAC system 100 may enter a defrost mode, wherein the HVAC system 100 heats the outdoor components of the HVAC system 100 by entering the cooling mode. That is, refrigerant flow is directed such that heat is removed from indoor zones (such as the zones 206, 208, 210, 212, 214, and 216) and is transferred to the portions of the outdoor unit 104 that may be subjected to frosting. For example, heat may be removed from the indoor zones and transferred to the outdoor heat exchanger 114 of the outdoor unit 104 to melt any accumulated frozen condensation on the outdoor heat exchanger 114. Supplemental heat may be added to the air supplied to the indoor zones while the defrost mode is active to prevent the supplied air from becoming uncomfortably cool at a time when warm air may be expected to be provided.

Entry into a defrost mode may be triggered by several different parameters, such as the ambient air temperature, the temperature of the outdoor heat exchanger 114, the difference between the ambient air temperature and the outdoor heat exchanger 114 temperature (which may be referred to as the delta T), the air pressure drop across the outdoor heat exchanger 114, the suction pressure, and/or the outdoor fan 118 power or current. A defrost mode may be terminated based on an outdoor heat exchanger 114 temperature threshold or another related parameter.

Such a defrost mode is typically sufficient to remove frost formed when water vapor in the ambient air freezes on the outdoor heat exchanger 114. However, in cases where there is a heavier buildup of ice on the outdoor heat exchanger 114, additional defrosting may be needed. Such cases may be indicated by an exceptionally high or exceptionally low delta T. When a heavy buildup of ice is indicated, a timed defrost mode may be entered, wherein a defrost mode is entered for a first predetermined length of time, stopped for a second predetermined length of time, and then re-entered for the first predetermined length of time. Such timed cycles of starting and stopping a defrost mode may continue for a predetermined number of cycles or may terminate when there is an indication that the ice buildup on the outdoor heat exchanger 114 has been alleviated.

In some cases, the ice buildup on the components of the outdoor unit 104 or other components of the HVAC system 100 may be exceptionally heavy. For instance, an ice storm may cause the outdoor heat exchanger 114 to become totally encapsulated in a thick layer of ice. As another example, melting ice dripping from a roof may fall on the outdoor heat exchanger 114 and then refreeze, causing an ice bridge to form between the outdoor fan 118 and other portions of the outdoor unit 104. The ice bridge may prevent operation of the outdoor fan 118, thereby potentially allowing greater ice formation. The timed defrost mode may not be sufficient to remove the ice when such extreme conditions occur, and the ice may not be removed until it melts naturally. If the timed defrost mode is terminated by an indication that the ice has been substantially eliminated from the outdoor heat exchanger 114, the indication may not occur for an extended period of time. Timed defrost cycles may continue throughout that time with little effect.

Cycling in and out of a defrost mode for an extended length of time may be detrimental to the compressor 116 and other components of an HVAC system 100. That is, initiation or termination of a defrost cycle of a heat pump system, such as HVAC system 100, may instantaneously reverse the pressures across the compressor 116. When such reversals occur and for a period of time afterwards, the compressor 116 may be exposed to liquid refrigerant, which increases the stress on the compressor 116. In addition, oil viscosity is diluted, which can lead to bearing damage. Further, liquid refrigerant is incompressible, and very high impact pressures may result if liquid refrigerant enters the compression mechanism of the compressor 116. Thus, it may be undesirable to repeatedly cycle in and out of a defrost mode for an extended period of time, particularly when it is unlikely that lengthy operation in the defrost mode will remove enough ice to allow a return to operation in the heating mode.

In an embodiment, techniques are provided for determining when an ice buildup on the outdoor components of an HVAC system 100 are so heavy that multiple cycles of a timed defrost mode are unlikely to sufficiently remove the ice. In an embodiment, the HVAC system 100 may be shut down when such circumstances occur. As used herein, terms such as “shut down” and the like may refer to preventing operation at least one major HVAC system component, such as a compressor 116 or an outdoor fan 118, that may be damaged by repeated cycles of a timed defrost mode. Some components, such as indoor fans, backup heaters, electronic processors, or fault notification systems, may continue to operate during the shut-down. As described in more detail below, the techniques for shutting down an HVAC system under extreme icing conditions may also be applied to other types of fault conditions, but the discussion herein focuses mainly on icing as the fault condition.

One parameter that may be used to indicate that an excessive coating of ice is present on the outdoor components of an HVAC system 100 is the rate of change of the delta T, that is, how quickly the difference between the ambient air temperature and the outdoor heat exchanger 114 temperature is changing. It is known that the rate of change of delta T for a normally operating system in a heavy frosting condition is approximately 0.002 degrees/degree/second. Under heavy icing conditions, there may be no airflow across the outdoor heat exchanger 114. In such conditions, the rate of change of delta T is approximately 0.040 degrees/degree/second, or a 20 times higher rate than under more typical conditions. Thus, in an embodiment, a rate of change of the delta T that exceeds a predefined threshold may be used to indicate that an ice coating on the outdoor components of an HVAC system 100 is heavier than is likely to be sufficiently removed by a timed defrost mode.

Other parameters that may be used to indicate that a heavy coating of ice is present on the outdoor components of an HVAC system 100 include the air pressure drop across the outdoor heat exchanger 114, the suction pressure, and/or the outdoor fan 118 power or current. For any such parameter, a threshold may be defined which, when crossed, indicates that a heavy buildup of ice exists on the outdoor components of an HVAC system 100 or that some other type of fault condition exists.

In another embodiment, a time-based procedure may be used to indicate that an outdoor component of the HVAC system 100 is covered with so much ice that a timed defrost mode is unlikely to sufficiently remove the ice. More specifically, when a heating cycle on a heat pump system begins, the system will typically enter the defrost mode more quickly when a heavy coating of ice is present on the outdoor components of the HVAC system 100 than when little or no frost is present. The timing of how soon the system enters the defrost mode after a heating cycle begins can thus be used as an indication that the outdoor components are heavily coated with ice. When a heavy buildup of ice is indicated in such a manner, it may be preferable to shut the system down rather than subject the system to multiple cycles of defrosting that are unlikely to be effective.

In an embodiment, the start of a defrost mode less than a predefined length of time, such as 15 minutes, after the start of a heating cycle may be taken as a preliminary indication that a heavy coating of ice is present on the outdoor components of an HVAC system 100. Since there may be other reasons for a defrost mode to start shortly after the beginning of a heating cycle, it may be preferable for a plurality of such preliminary indications to occur consecutively before a more definitive indication is assumed. In an embodiment, a count is kept of how many consecutive times a defrost mode begins less than the threshold time after the start of a heating cycle. When the count reaches a threshold count, such as three consecutive times, the HVAC system is temporarily shut down for a predefined length of time, such as 15 minutes. That is, at least one of the major outdoor components of the system, such as the compressor 116 or the outdoor fan 118, is temporarily not allowed to operate. If the threshold count has not yet been reached and a defrost mode begins longer than the threshold time after the start of a heating cycle, the threshold count is reset to zero. This ensures that a plurality of preliminary indications of an ice buildup must occur consecutively in order for the more definitive indication to be assumed.

In some cases, the temporary shutdown may alleviate the situation that was causing a defrost mode to repeatedly begin less than the threshold time after the start of a heating cycle. Thus, it may be preferable for a plurality of such temporary shutdowns to occur consecutively before a final indication of excessive icing on the outdoor components of the HVAC system 100 is assumed. In an embodiment, a count is kept of how many temporary shutdowns occur. When the count reaches a threshold count, such as three consecutive temporary shutdowns, a final indication is assumed that the outdoor components of the HVAC system 100 are so heavily iced over that further defrost cycles are unlikely to be effective.

In such a case, the HVAC system 100 is unlikely to function properly, so there may be no point in continuing to operate the system. Thus, in an embodiment, when the number of temporary shutdowns reaches the shutdown threshold, the HVAC system 100 is shut down completely to prevent the stress that would be placed on the compressor 116 and other components in performing futile defrosts. Shutting the HVAC system 100 down completely may refer to preventing at least one of the major outdoor components of the system, such as the compressor 116 or the outdoor fan 118, from operating until the ice buildup is alleviated enough for a defrost mode to produce a typical level of effectiveness. The ice may be removed by an owner or operator of the HVAC system 100, by a technician, by natural melting, or in some other manner. If the fault condition was caused by something other than an ice buildup, then the fault condition may need to be alleviated before the HVAC system 100 is allowed to restart. In an embodiment, the HVAC system 100 may provide some indication that it has locked itself out and that a technician may need to be called or some other action may need to be taken to alleviate the fault condition.

FIG. 3 is a flowchart of a method 300 for operating an HVAC system, such as HVAC system 100. At block 310, a timer is started when a heating cycle begins. At block 320, the system enters a defrost mode some length of time after the heating cycle begins, and the timer is stopped. At block 330, the value of the timer is read to determine if the defrost mode began less than 15 minutes after the heating cycle began. In other embodiments, other threshold values for the timer could be used. If the defrost mode began less than 15 minutes after the heating cycle began, then at block 340, a first counter that keeps track of how many consecutive times the defrost mode began less than 15 minutes after the heating cycle began is incremented. If the defrost mode began 15 minutes or more after the heating cycle began, then at block 345, the first counter and a second counter described below are reset to zero. The procedure then returns to block 310, and additional values are recorded for the time between the beginning of a heating cycle and the beginning of a defrost mode.

After the first counter is incremented at block 340, a determination is made at block 350 whether the first counter is equal to three. That is, it is determined whether three consecutive occasions have occurred in which a defrost mode began less than 15 minutes after a heating cycle began. In other embodiments, other values could be used for the threshold for the first counter. If the first counter does not equal three, the procedure returns to block 310, and additional values are recorded for the time between the beginning of a heating cycle and the beginning of a defrost mode. If the first counter does equal three, the HVAC system is shut down for 15 minutes at block 360. In other embodiments, other lengths of time could be used for the temporary shutdown.

At block 370, after the temporary shutdown ends, a second counter that keeps track of how many temporary shutdowns have occurred is incremented. The first counter is reset to zero so that it will again be ready to start counting how many times the timer threshold is reached. Alternatively, the procedures at block 370 may occur before the procedures at block 360. At block 380, a determination is made whether the second counter is equal to three, indicating that three consecutive temporary shutdowns have occurred. In other embodiments, other values could be used for the threshold for the second counter. If the second counter does not equal three, the procedure returns to block 310, and additional values are recorded for the time between the beginning of a heating cycle and the beginning of a defrost mode.

If the second counter does equal three, the typical heating mode and cooling mode of the HVAC system are shut down completely at block 390. That is, at least one of the major outdoor components of the HVAC system 100 that may be damaged by continued use, such as the compressor 116 or the outdoor fan 118, are no longer allowed to operate at all. Some components, such as indoor fans or backup heaters, may be allowed to continue to operate. The HVAC system 100 may not be allowed to re-enter the typical heating mode or cooling mode until a technician repairs the problem or some other procedure is performed to alleviate the fault condition.

In other embodiments, a similar shutdown procedure may be used to shut an HVAC system 100 down when other major fault conditions occur, such as a high rate of change of delta T, a loss of airflow across the outdoor unit for a reason other than a buildup of ice, a loss of refrigerant, a low suction pressure, or a failure of the outdoor fan 118. In such embodiments, the procedures at blocks 310, 320, and 330 in FIG. 3 may be replaced by the detection of the relevant fault condition. The remaining procedures in FIG. 3 may then be followed, wherein the HVAC system 100 is shut down temporarily when a fault condition is detected a plurality of times consecutively, a count is maintained of how many consecutive times the system is temporarily shut down, and after a plurality of consecutive temporary shutdowns, the system is completely shut down. That is, components of the system that may be damaged by continued use are prevented from operating until the fault condition is alleviated.

As an example, if the rate of change of delta T exceeds a predefined threshold in a predefined number of consecutive measurements, the HVAC system 100 may be shut down temporarily. If a predefined number of consecutive temporary shutdowns occur, the HVAC system may be shut down completely.

FIG. 4 illustrates a typical, general-purpose processor (e.g., electronic controller or computer) system 1300 that includes a processing component 1310 suitable for implementing one or more embodiments disclosed herein. In some embodiments, system controller 106 may comprise the general-purpose processor system 1300. In addition to the processor 1310 (which may be referred to as a central processor unit or CPU), the system 1300 might include network connectivity devices 1320, random access memory (RAM) 1330, read only memory (ROM) 1340, secondary storage 1350, and input/output (I/O) devices 1360. In some cases, some of these components may not be present or may be combined in various combinations with one another or with other components not shown. These components might be located in a single physical entity or in more than one physical entity. Any actions described herein as being taken by the processor 1310 might be taken by the processor 1310 alone or by the processor 1310 in conjunction with one or more components shown or not shown in the drawing.

The processor 1310 executes instructions, codes, computer programs, or scripts that it might access from the network connectivity devices 1320, RAM 1330, ROM 1340, or secondary storage 1350 (which might include various disk-based systems such as hard disk, floppy disk, optical disk, or other drive). While only one processor 1310 is shown, multiple processors may be present. Thus, while instructions may be discussed as being executed by a processor, the instructions may be executed simultaneously, serially, or otherwise by one or multiple processors. The processor 1310 may be implemented as one or more CPU chips.

The network connectivity devices 1320 may take the form of modems, modem banks, Ethernet devices, universal serial bus (USB) interface devices, serial interfaces, token ring devices, fiber distributed data interface (FDDI) devices, wireless local area network (WLAN) devices, radio transceiver devices such as code division multiple access (CDMA) devices, global system for mobile communications (GSM) radio transceiver devices, worldwide interoperability for microwave access (WiMAX) devices, and/or other well-known devices for connecting to networks. These network connectivity devices 1320 may enable the processor 1310 to communicate with the Internet or one or more telecommunications networks or other networks from which the processor 1310 might receive information or to which the processor 1310 might output information.

The network connectivity devices 1320 might also include one or more transceiver components 1325 capable of transmitting and/or receiving data wirelessly in the form of electromagnetic waves, such as radio frequency signals or microwave frequency signals. Alternatively, the data may propagate in or on the surface of electrical conductors, in coaxial cables, in waveguides, in optical media such as optical fiber, or in other media. The transceiver component 1325 might include separate receiving and transmitting units or a single transceiver. Information transmitted or received by the transceiver 1325 may include data that has been processed by the processor 1310 or instructions that are to be executed by processor 1310. Such information may be received from and outputted to a network in the form of, for example, a computer data baseband signal or a signal embedded in a carrier wave. The data may be ordered according to different sequences as may be desirable for either processing or generating the data or transmitting or receiving the data. The baseband signal, the signal embedded in the carrier wave, or other types of signals currently used or hereafter developed may be referred to as the transmission medium and may be generated according to several methods well known to one skilled in the art.

The RAM 1330 might be used to store volatile data and perhaps to store instructions that are executed by the processor 1310. The ROM 1340 is a non-volatile memory device that typically has a smaller memory capacity than the memory capacity of the secondary storage 1350. ROM 1340 might be used to store instructions and perhaps data that are read during execution of the instructions. Access to both RAM 1330 and ROM 1340 is typically faster than to secondary storage 1350. The secondary storage 1350 is typically comprised of one or more disk drives or tape drives and might be used for non-volatile storage of data or as an over-flow data storage device if RAM 1330 is not large enough to hold all working data. Secondary storage 1350 may be used to store programs or instructions that are loaded into RAM 1330 when such programs are selected for execution or information is needed.

The I/O devices 1360 may include liquid crystal displays (LCDs), touch screen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, printers, video monitors, transducers, sensors, or other well-known input or output devices. Also, the transceiver 1325 might be considered a component of the I/O devices 1360 instead of or in addition to being a component of the network connectivity devices 1320.

At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R_(l), and an upper limit, R_(u), is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R_(l)+k*(R_(u)−R_(l)), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as “comprises”, “includes”, and “having” should be understood to provide support for narrower terms such as “consisting of”, “consisting essentially of”, and “comprised substantially of”. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. 

What is claimed is:
 1. A method of operating a heating, ventilation, and/or air conditioning (HVAC) system, comprising: detecting a fault condition in response to the HVAC system to entering a defrost mode before a predefined threshold is reached for a predefined number of consecutive occasions; and preventing operation of at least one component of the HVAC system for a predefined length of time in response to detecting the fault condition.
 2. The method of claim 1, further comprising: preventing operation of at least one component of the HVAC system until the fault condition is alleviated in response to detecting the fault condition a predefined number of fault condition occurrences.
 3. The method of claim 1, further comprising: incrementing a first counter in response to the HVAC system entering the defrost mode before the predefined threshold time.
 4. The method of claim 3, further comprising: incrementing a second counter in response to detecting the fault condition.
 5. The method of claim 4, further comprising: preventing operation of at least one component of the HVAC system in response to incrementing the second counter a predetermined number of times.
 6. The method of claim 5, wherein the predefined threshold comprises a predefined length of time after entering a heating cycle.
 7. The method of claim 1, wherein the predefined threshold comprises a rate of change of a difference between an ambient air temperature and an outdoor heat exchanger temperature.
 8. The method of claim 1, wherein the fault condition comprises at least one of: an air pressure drop across the outdoor heat exchanger; a suction pressure; and an outdoor fan power or current.
 9. The method of claim 1, further comprising: providing a notification of the fault condition.
 10. A heating, ventilation, and/or air conditioning (HVAC) system, comprising: a system controller configured to: detect a fault condition in response to the HVAC system to entering a defrost mode before a predefined threshold is reached for a predefined number of consecutive occasions; and prevent operation of at least one component of the HVAC system for a predefined length of time in response to detecting the fault condition.
 11. The HVAC system of claim 10, wherein the controller is further configured to prevent operation of at least one component of the HVAC system until the fault condition is alleviated in response to detecting the fault condition a predefined number of fault condition occurrences.
 12. The HVAC system of claim 10, wherein the controller comprises a first counter configured to increment each time the HVAC system enters the defrost mode before the predefined threshold time.
 13. The HVAC system of claim 10, wherein the controller comprises a second counter configured to increment each time the controller detects a fault condition.
 14. The HVAC system of claim 13, wherein the controller is configured to prevent operation of at least one component of the HVAC system in response to incrementing the second counter a predetermined number of times.
 15. The HVAC system of claim 10, wherein the predefined threshold comprises at least one of: a predefined length of time after entering a heating cycle; a rate of change of a difference between an ambient air temperature and an outdoor heat exchanger temperature; an air pressure drop across the outdoor heat exchanger; a suction pressure; and an outdoor fan power or current.
 16. The HVAC system of claim 10, wherein the controller is further configured to provide a notification of the fault condition.
 17. A method for operating a heating, ventilation, and/or air conditioning (HVAC) system, comprising: recording a number of consecutive occasions in which a defrost mode is entered within a first predefined length of time after a heating cycle is entered; preventing operation of at least one component of the HVAC system for a second predefined length of time in response to entering the defrost mode a first predetermined consecutive number of occurrences within the first predefined length of time after a heating cycle is entered; recording a number of consecutive preventions of operation of the component of the HVAC system; and determining that a fault condition exists in the HVAC system in response to the number of consecutive temporary preventions of operation of the component of the HVAC system exceeding a second predefined number of occurrences.
 18. The method of claim 17, further comprising: preventing operation of at least one component of the HVAC system down until the fault condition is alleviated.
 19. The method of claim 17, further comprising: providing a notification of the fault condition.
 20. The method of claim 17, wherein the predetermined consecutive number of occurrences and the second predefined number of occurrences is three. 